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Thomas Aquinas Thomas Aquinas
• Lived 1225-1274AD.• The Catholic church came to prominence
around 500AD—1500AD.• Christianity was the dominant religion.• Aquinas was one of the greatest
interpreters of Aristotle’s work.• He showed that Aristotle’s views could be
reconciled with Christianity.
Thomas Aquinas
• In Aristotle we see a division amongst the animals by way of the kind of soul they possess—nutritive, sensitive, rational.
• This is a hierarchical ordering.• The Scala Natura—The Great Chain of
Being.
The Scala Natura—The Great Chain of Being
• Pure Actuality (Prime Mover)– Humans (Rational)– Animals (Sensitive)– Plants (Nutritive)– Non-living natural objects (e.g. rocks, bone..)– The elements (earth, air, fire, water)
• Pure substance/Pure Potentiality
The Scala Natura—The Great Chain of Being
• For Aquinas, things were ordered in the world according to their perfection and reflecting God’s plan.
• Humans are close to the top of the chain of being, with God at the very top.
• Everything has a purpose (teleology)—God is the Final Cause of all in the world.
• The Great Chain of Being reflects God’s plan.• Thus, the Aristotelian world-view is consistent
with Christianity.
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The Scientific
Revolution
Nicolas Copernicus (1473-1543)
Nicolas Copernicus
• Up until Copernicus’ publication of On the Revolutions of the Heavenly Bodies, the Ptolemaic (90-168AD) model of the universe was dominant theory.
• Ptolemy’s model was a detailed mathematical account of the orbits of the planets that was geocentric (earth at the center).
• Aristotle presented a geocentric cosmology earlier than Ptolemy.
Nicolas Copernicus
• Copernicus revolutionized the way we viewed the planetary system by proposing that the sun was the center of the (known) universe—heliocentric model of the universe.
• This upset a great deal of traditional thinking.
• Cosmology was tied to the notion of the Great Chain of Being.
Nicolas Copernicus
• The Earth was the focus of God’s creation an as such was held to be the center universe—God’s plan.
• As such his view was rejected by the Church.• But it inaugurated an enormous shift in our
thinking about the world.
Francis Bacon (1561-1626)
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Francis Bacon• Bacon ushered in a new way of thinking about how we
ought to go about understanding the world.• It was the first articulation of the scientific method—in his
Novum Organon—a play on Aristotle’s Organon.• Bacon was deeply critical of the ancients and challenged
the fundamental form of reasoning they used in the acquisition of knowledge—the deductive method.
• He argued that there had been little progress to our understanding of the world and that a reform was required.
Francis Bacon• In the place of deduction, he argued for an
inductive method of inquiry.• Scientific reasoning is still held to be a form of
inductive reasoning. • The goal was, through experience, to collect
facts in an unbiased way.• Then on the basis of an analysis of these facts
we proceed to make modest generalizations about the nature of the world—inductive generalizations!
Francis Bacon
• In outline, this is an articulation of the basic tenets of the scientific method—observation, experimentation and generalization.
Challenging Aristotelian Science
• Aristotle’s explanation of change and motion were informed by his cosmology.
• As a result of Copernicus’ revolutionary changes to the model of the universe, central portions of Aristotle’s scientific system fell apart.
• During this period of scientific innovation, Aristotle’s schema of matter and form also came under challenge.
Challenging Aristotelian Science
• Critics argued that the claims became empty when applied to complex problems.
• E.g. Aristotelians might say that sleeping powder achieves its result because it possesses “sleep qualities”—that which is potentially asleep becomes actually asleep in the presence of these qualities.
• But this doesn’t really help explain how the powder works.
Challenging Aristotelian Science• Similar arguments can be presented against the
definition of the soul.• Recall, the soul is the form of living things.• But the form is also that which makes something
the kind of thing it is.• Put these together and what Aristotle seems to
be saying is that soul is that which brings life to living things.
• All true…but not very helpful.• We want to know how the soul does this.
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Challenging Aristotelian Science
• Apart from these internal problems to the Aristotelian system, it also faced new challenges presented by a new approach to science.
• Most significantly, the new science rejected Aristotle’s explanations of cause and effect.
• Change for Aristotle was explained in terms of things taking on forms and qualities.
Challenging Aristotelian Science• Things move towards the full realization of
respective forms and qualities.• E.g. the acorn becomes an oak because it has
the form built into it (its purpose/final cause is to become an oak)
• Similarly, the earth is “heavy” because its proper place is the centre of the cosmos, so it will naturally move there.
• Similarly, fire moves upwards towards its natural place in the outer regions.
Challenging Aristotelian ScienceMechanical Explanations• Thinking of causation in these purposeful ways
is to think in terms of teleological explanations(ends, goals, purpose).
• Compare this with modern ideas of motion.• Law of inertia: in the absence of external force
an object will maintain a constant state of rest or uniform motion.
• Matter is inert—it has no natural direction of motion, or internal drive.
Challenging Aristotelian Science
• In modern physics, motion is explained by external forces acting on objects—which will maintain there current state in the absence of such forces.
• These are mechanical explanations.• A distinctive feature of the scientific
revolution occurring in the 1600s was the rejection of teleological explanation for mechanical explanation.
Challenging Aristotelian Science• Part of the reason for this was the emptiness of
Aristotelian explanations.• There’s no point in explaining change in terms of
goals etc., if the goal is just a re-description of the change—we already know that it changes, we want to know why.
• E.g. to explain falling objects by saying that they naturally fall, isn’t much help.
• The forces proposed by mechanical explanations seemed better suited.
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Challenging Aristotelian ScienceMathematical Laws• The new science also placed a great deal of
emphasis on mathematics as a tool for describing natural laws.
• Aristotle’s system was qualitative in nature—explaining change as changes in qualities—no mathematics.
• A distinctive feature of the new science was the formulation of mathematical laws and the replacement of qualitative descriptions with quantitative ones (time, weight, distance…).
• E.g. v = d/t
Challenging Aristotelian Science• Platonic revival—the relationship between
mathematics and nature.• As Aristotelian science became more
problematic, scholars in the middle ages returned to this Platonic notion.
• E.g. Copernicus on his heliocentric model… “we find then in this arrangement an admirable harmony of the world, and a dependable, harmonious interconnection of the motion and size of the paths, such as otherwise cannot be discovered.”
Galileo Galilei (1564 – 1642) Galileo Galilei
• Galileo challenged the dominant Aristotelian theory of motion with his detailed studies of the times and motions of falling bodies.
• Famous canon-ball/musket-ball experiment at the Tower of Pisa.
• Also performed various pendulum and rolling ball experiments to show that Aristotelian theory of motion was inconsistent with the observable facts.
Galileo Galilei
• Galileo had adopted the new science and its mechanical and mathematical explanations to explain motion.
• As a result of his work, he faced increasing criticism by the Aristotelians, who were, not surprisingly on the side of the Church.
• In 1663 he was imprisoned by the Inquisition for teaching Copernicus’ theory.
Galileo Galilei
• The Aristotelians said “that as he became a better mathematician he became a worse physicist, because he moved away from the world as it appears in simple observations, and focused instead on abstract and ideal mathematical descriptions of times and motions.”
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Challenging Aristotelian Science (Again)
• This shift in thinking also did damage to Aristotelian confidence in the reliability of perception.
• Mathematical laws are idealizations of what we actually observe.
• The acceptance of mathematical laws did not follow from their observability, but from the fact that they produced better predictions.
Challenging Aristotelian Science (Again)
• This led the new scientists to think that the real qualities of objects are not necessarily the ones we perceive.
• Thus, appearances (observation) may not be the ultimate guide to understanding the world—even though it is the appearances we want explained.
• And this ushered in new challenges to Aristotle’s account of the relation between the perceiving mind and the physical world—that the real qualities of objects are not like the sensations we experience.
Galileo AgainAn Argument Against Aristotelian Perception• Aristotle thought the qualities we perceive are
features of the objects of perception.• Galileo argues that this is a misattribution of
things we know with our mind to the objects themselves.
• Imagine being tickled lightly by a hand or a feather.
• Everyone agrees the tickling belongs to us and not to the hand. Right?
Galileo Again
• If we run our hand over a statue, no one thinks the statue feels a tickle.
• Thus, the tickling is not a property of the hand (or feather).
• It exists solely in the mind of the person being tickled.
• The same goes for the other senses.• Objects produce the sensation in us, but the do
not possess sensation.
Galileo Again
• Galileo explained it instead as a result of the motion of particles of matter.
• For example, he suggests that sensations of sound are the result of moving air particles causing a vibration on the eardrum.
• Differences in vibration differences in the sensation of sound in the mind.
Galileo Again
• For this and other reasons, Galileo thought that the only qualities that really exist in material objects are the sizes, shapes, and motions of the particles that cause sensations.
• Tastes, odours, sounds, are merely sensations in our minds.
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Rene Descartes Rene Descartes
• Lived (1596-1650).• Francis Bacon (1561-1626).• Galileo Galilei (1564 – 1642).• Descartes was also an influential figure in
the new science.• He was part scientist, part mathematician,
part philosopher.
Rene DescartesThe Meditations• Descartes was obsessed with the idea that
scientific progress required that we have a means of examining all beliefs—to separate those notions that are reliable from those that are not.
• In short, his goal was to find a secure foundation for all of our knowledge.
• This is Descartes’ Foundationalism.• Like Galileo, he challenged the idea that
appearances should be the primary source of information about the world.
Rene Descartes• This was to be achieved by the systematic rejection of
any assumptions that could possibly be called into doubt.• And on the basis of the foundation and reason alone
(logic) we would secure (deduce) all knowledge.• Descartes was Rationalist.• How to doubt? Methodological Skepticism.• There are two main arguments used to call all that we
can into doubt.
(1) The Dreaming Argument.(2) The Deceiver Argument.
Rene DescartesThe Cogito• Given what has been set out in the previous
arguments Descartes/the reader now has grounds to doubt all his/her knowledge.
• So where is this foundation that Descartes intended to find?
• All he needs (like Archimedes) is one point that is “certain and unshakeable” to found his knowledge upon.
• But, we have already doubted everything…what could possibly remain?
Rene Descartes
• The one thing that seems difficult to doubt is that, there is some doubting going on.
• Cogito ergo sum: “I am thinking, therefore I exist.”
• This is the foundational piece of knowledge Descartes was looking for.
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From the Mind Onward
• What is a thinking thing?• It doubts, understands, affirms, denies, is
willing, imagines, perceives…but do all of these attributes really belong to us?
• They are all merely kinds of thinking. • So, these ruminations support the idea
that the essence of the mind is thinking—it is a thinking substance.
From the Mind Onward
• What can we know about the external world?• Consider a piece of beeswax.• Examine its sensible qualities.• Tastes like honey; Smells like flowers; has
distinct colour, shape, size…• Now place it near a fire.
From the Mind Onward
• Once again, let’s examine its sensible qualities.
• The taste is gone; the smell is gone; the colour and shape have changed, it’s larger in size…
• So what is essential to the wax?• It can’t be these sensible qualities since
they have all disappeared.
From the Mind Onward
• But we still see that the wax continues to exist without them.
• These are merely accidental features of the wax.
• What we can say, at the very least, is that the wax takes up space—that it is extended in general (it has extension).
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From the Mind Onward
• How do we know this? • The senses never give us a notion of
general extension because all objects come with a particular shape, size etc.
• Extension is grasped by the understanding not through our senses.
• So the essential feature of bodies is that they are extended…and this we know via the understanding.
From the Mind Onward
• But Descartes realizes that he still can’t be certain of these claims.
• Thus, he ushers in (non-deceiving) God as a means of justifying these ideas.
• This is the antidote to the deceiver argument.
• I will leave aside the argument for the existence of God.
From the Mind Onward• Once we accept that a non-deceiving God exists
(since deception would be contrary to his nature), then we can prove the certainty of our knowledge.
• Thus, those ideas that are clear (i.e. vivid) and distinct must also be true, for, if they were not, God would be a deceiver.
• In this way, the existence of God validates many of the ideas that we have.
• Thus, clear and distinct ideas cannot be doubted, and they become our source of knowledge.
From the Mind Onward
• Some of these clear and distinct ideas are built into us—e.g. mathematical ideas.
• These are innate ideas: a perennial issue in psychology.
Descartes’ Dualism
• So now we have two kinds of substances: thinking substances and extended substances.
• The essence of the mind is that it is a thinking substance and the essence of material bodies is that they are extended in space.
• On the basis of this Descartes claims that the mind is distinct from the body—mind/body dualism.
Descartes’ Dualism1. “The fact that I clearly and distinctly
understand one thing apart from another is enough to make me certain that the two things are distinct.”…otherwise God is a deceiver.
2. I have a clear and distinct idea of myself as existing without a body…the essence of mind is thought…the essence of body is extension.
3. Therefore, I am not my body (or God is a deceiver).Mind and body are distinct! Platonism again.
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Descartes’ Dualism
• Descartes thought that the pineal gland was where the soul was located.
• The reason for this was that all of the other parts of the brain are double.
• The pineal gland represented was a single structure that couldhouse the soul—a unitary object.
Descartes Dualism• Gilbert Ryle (1949) referred Descartes view as the
“ghost in the machine.”• As a result of these commitments we can also describe
Descartes as an interactionist—since the immaterial mind must be supposed to interact with a material body.
• This led to the Mind/Body problem that has been with us since (Behaviourism/Cognitive Science).
• Descartes also assumed that we know things best through the understanding (mind), and thus the key to knowledge was introspection.
• This became the foundation for later introspective psychologists (William James).
Descartes and the Body
• Descartes also believed the mind to operate according to its own rules, given by God, while the body is subject to mechanical laws.
• Descartes conceived of the body as a kind of mechanical device (machine)—this was informed by some of the latest technological and scientific developments of the day.
Descartes and the Body• The fire (A) displaces
the skin, which pulls a tiny thread (B), which opens a pore in the ventricle (F) allowing the "animal spirit" to flow through a hollow tube, which inflates the muscle of the leg, causing the foot to withdraw.
Descartes and the Body
• The development of various tinker toys that mimicked animal actions were inspiring (e.g. Vaucanson’s duck).
• This led to thinking of organisms as machines and gave rise to the possibility of building machines indistinguishable from animals.
• This gave rise to the possibility of artificial life, robotics, and artificial intelligence.
Vaucanson’s Duck
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Descartes and the Body• Though Descartes was skeptical that such
innovations would lead to mimicking human behaviour (Turing Test), he did think it was possible in the case of animals.
• Though he though humans and animals were different, he saw no difference between animals and machines…the were automatons.
• This mechanical approach to the body would, in later history, be adopted as an approach to the mind.
More on Descartes• Descartes had detailed theories about the
nature of perception.• He developed the first comprehensive account
of the role of emotion in mental life (The Passions of the Soul).
• He worked to develop a theory of mind/body interaction—which he later integrated with his account of the passions.
• Developed a robust methodology for inquiry.• He had an elaborate cosmology.
Isaac Newton (1642-1727) Isaac Newton
• Has been described as the ‘greatest scientific genius the English-speaking peoples have produced.’
• He studied everything from alchemy to history.• His most famous work is his Principia—in which
he lays the foundation for classical physics.• Interestingly, he spends a great deal of time
attacking the cosmology of Descartes, which was the going theory.
Isaac Newton• One of Newton’s greatest discoveries were his
basic laws of motion.• E.g. The law of inertia (Law 1).• These were expressed in mathematical terms
(recall Pythyagoras).• The fact that all motion (from the planets to small
objects) can be captured by these basic laws was extremely profound—physics unified science.
• It suggested that the world was governed by these basic immutable (mathematical) laws.
Isaac Newton• Science is an attempt to provide general
explanations of this sort.• Psychology as a science strives to discover the
laws of human behaviour, thought, perception, etc.—psychological laws.
• Further, many psychologists have attempted to emulate the physical sciences by treating psychological events as physical events that follow the same laws that regulate other physical systems.
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Isaac Newton• In this way, psychology as a subject matter is treated
essentially the same as physics—both study the motion of physical systems (motion of objects vs. motion of organisms—behaviour).
• Just as force is required to move physical objects (given the law of inertia), it is also required to move organisms.
• And not just any force is sufficient (follows from second law of motion), it must be a strong enough force to initiate motion (e.g. pushing a dump-truck).
• Force must exceed a threshold (neuronal excitation; awareness; hearing…).
Isaac Newton• Newton also did work in optics—which was an attempt to
give a physical understanding of light and colour phenomena.
• His prism experiment showed that light actually could be split into different kinds of light—that white light is a composite of other colours.
• He did not think that light had these properties, but it had the power (disposition) to create the subjective experience we have of colours.
• Stimulus vs. subjective experience.• A physical description will not exhaust our subjective
experience.• Recall Galileo.
Next Class
• The British Empiricists• Kant• Maybe Mill and Wolstonecraft.